1. Field of the Invention
The invention relates to a rotating printing device and process for printing on a web which is continuously fed off of a reel.
2. Description of Prior Art
Rotating printing processes, such as rotogravure, are well known and are used to reproduce drawings and various graphical illustrations and the like. Typically, the desired illustration is engraved on the cylindrical form of a printing cylinder coated with a product, such as a printing liquid, which is transferred onto a moving and continuous web of suitable material as the printing cylinder rotates. Such processes may further be used to provide flat coatings.
The cylindrical forms of the printing cylinders can be intaglio engraved (heliograph) or be engraved in relief (typography, flexograph). The printing or the coating of the web can be achieved by means of various products which are suitable to achieve the desired results, e.g., printing inks, carbons, self-adhesives, thermo-fusible glues, chemical coatings for self-reproductive papers, i.e., carbon paper and pressure sensitive paper, or for papers known as "chemical" papers, etc.
The product is transferred onto the web from a product container in which a rotating cylinder is submerged. The rotating cylinder can be a printing cylinder which is intaglio engraved (heliograph) or a takeup cylinder coating the forms in relief carried by a cliche-carrying cylinder by means of a touching cylinder (typography, flexography). The product, remaining in the grooves of the intaglio engraved printing cylinder after wiping of the engraved cylinder by means of a wiper supported along one of its edges, is deposited on the web which, at the end of the procedure, is placed in intimate contact with the engraved printing cylinder. For typography or flexography, the raised portions of the printing cylinder are coated and the product transferred to the web in the same manner as in heliography. In each case, a contact zone is formed between the web and a press or press roller, coated with rubber and subjected to pressure of a hydraulic or mechanical nature, which presses the web against the product coated printing cylinder thereby transferring the product to the web.
So that the product exhibits satisfactory physical and/or chemical characteristics, it is often necessary to determine and impose a very precise temperature at the moment of deposition on the web. This is the case particularly for carbons, thermo-fusible glues, and the emitting and receiving coatings of chemical paper. The cold viscosity of the product can, furthermore, necessitate a heating during the storage of the product in the container and during the entire transfer procedure (this is particularly true of thermo-fusible glues).
In all cases, too sudden variations of temperature of the product can cause irreversible modification of the product. This is of particular importance in the course of the transfer of the product, i.e., during the period where the product is subjected to the differing temperatures of various roller and feed arrangements.
It has thus been proposed to maintain the temperature of the product storage container, the cylindrical form of the printing cylinder, the press roller and each of the complementary product modifying or preparing elements of the cylindrical form, such as the wiping blades for heliogravure or the takeup cylinder and touching cylinder for typography or flexography. However, this feature is accomplished by thermostatic regulation of each of the elements independently of one another by means of oil baths and heating sticks. This solution is not very satisfactory, because of the high consumption of energy due to a significant loss of heat into the ambient air. Additionally, disadvantages are experienced because one does not totally overcome the variations of temperature from one element to another due to the dispersion and the conduction of heat from one element to another.
A rotating printing device comprises an enclosure containing a printing cylinder. The enclosure includes the window and the device also incorporates a press which is adapted to support a web on which a product is to be applied. The window allows passage of at least a portion of the press into the enclosure and the press is adapted to form a contact zone with the web and to apply the contact zone against the printing cylinder. A container is adapted to contain the product for application to the printing cylinder and is enclosed by the enclosure. Gas flow means are included for providing a flow of gas having a predetermined temperature in the enclosure. The contact zone is positioned within the flow of gas such that the temperature within the product container and the temperature of the contact zone are substantially equal.
The process for temperature control is provided which uses a rotating printing device including an enclosure containing a printing cylinder. The enclosure encloses at least a portion of the press in which a product is to be applied. The press is adapted to provide a contact zone between the web and the printing cylinder, which is supplied with product from a container which is also enclosed by the enclosure. The process comprises the step of forming a flow of gas at a predetermined temperature in the enclosure to maintain the temperature of the contact zone as well as the product of the container at substantially the same temperature.